Conventional distortion correcting methods and devices, especially conventional distortion correcting methods and devices configured and employed for signal predistortion, compute linearization parameters for signal treatment off-line in software-executing circuitry. Such off-line software treatment contributes to slow adaptation time as compared with the period of the signal being treated, such as a radio frequency (RF) signal. As a result, longer term variations are compensated by the distortion correcting device, but shorter term variations are not addressable because of the slow adaptation time of the method and apparatus.
By way of example and not by way of limitation, a distortion compensation device such as a signal predistortion device may be employed in a mobile telephone network within a transceiver station at a remote location. Various environmental and operational parameters may be present in such a location. Slow changing parameters may include changes in the temperature within the equipment cabinet as the sun rises and sets, and changes in temperature as the equipment within the cabinet operates at higher or lower levels. As temperature changes, gain of transistors may change, matching networks and other linear circuit components may change response characteristics and other circuitry operational characteristics may be altered. Such a relatively slow-changing parameter as temperature change may be appropriate for predistortion signal handling by conventional devices.
Other changes experienced by equipment may be a change in power supply parameters when air conditioning equipment turns on or turns off. Such a temperature or power level change may be too short in duration to be adequately compensated by conventional predistortion signal handling devices to meet industry standards relating to purity and stability of signaling. As an example, such standards have been imposed by the Federal Communications Commission (FCC).
There is a need for a near-real time adaptive capability for predistortion signal handling devices that permits rapid response to environmental and other changes affecting operation of a signaling system.